I just thought I'd share my recent experience. I'm very illiterate when it comes to cars and have only recently taken an interest in my own maintenance. My 2008 Edge was driven across the country with a tow package (so about 3000 miles). I originally figured that that wouldn't be such a big deal. With the suggested 150k change in the manual I figured I'd easily be good till 60k since my towing was limited to my move. So when getting the oil changed my friend who was showing me how to do it (aforementioned nub status) he accidentally started pouring stabilizer in the transmission oil. It wasn't much but I had transmission problems with my old car so I wasn't taking any chances. We ended up flushing the transmission and just for being a bit over 30k it was black beyond belief.
After that experience I'll probably just flush it every 30k miles regardless.
